A Study of 48depl Ca 100 MoO 4 Scintillation Crystals for the AMoRE-I Experiment

Advanced Molybdenum-based Rare process Experiment (AMoRE) searching neutrinoless double-beta ( $0\nu \beta \beta $ ) decay of 100 Mo from 48depl Ca 100 MoO 4 (CMO) scintillation crystals has been preparing CMO crystals for the phase-I stage, AMoRE-I. Nine CMO crystals with a total weight of 3.39 kg were produced by the FOMOS-Materials in Russia and delivered to the Yangyang Underground Laboratory (Y2L) in South Korea for about 2 years until the end of 2016. Acceptance tests of all the nine crystals on weight, dimension, transmittance, light output, energy resolution, and internal radioactivities were completed in the middle of 2017. We have set the upper limits of internal radioactivity levels for 228 Th, 226 Ra, and 227 Ac (daughters of 232 Th, 238 U, and 235 U), and the total alpha activity of U/Th in the crystals via a GEANT4 Monte Carlo simulation to achieve zero background in region of interest. We used a delayed-coincidence analysis to separate the alphas from gamma background events. Results of the acceptance tests showed that all the crystals are qualified for the AMoRE-I. We will present the test results of the nine crystals together with a reference crystal.